1. Field of the Invention
The present invention relates to a composite type thin film magnetic head constructed by stacking an inductive type writing magnetic transducing element and a magnetoresistive type reading magnetic transducing element on a substrate.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. A composite type thin film magnetic head is constructed by stacking an inductive type thin film magnetic head intended for writing and a magnetoresistive type thin film magnetic head intended for reading on a substrate, and has been practically used. In general, as a reading magnetoresistive element, an element utilizing anisotropic magnetoresistive (AMR) effect has been used so far, but there has been further developed a GMR reproducing element utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than that of the normal anisotropic magnetoresistive effect by several times. In the present specification, elements exhibiting a magnetoresistive effect such as AMR and GMR reproducing elements are termed as a magnetoresistive reproducing element or MR reproducing element.
By using the AMR reproducing element, a very high surface recording density of several gigabits/inch.sup.2 has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes.
A height (MR Height: MRH) of a magnetoresistive reproducing element is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. The MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH can be obtained by controlling an amount of polishing the air bearing surface.
At the same time, the performance of the recording magnetic head is also required to be improved in accordance with the improvement of the performance of the reproducing magnetic head. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a write gap at the air bearing surface has to be reduced to a value within a range from several micron meters to several sub-micron meters. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head.
One of factors determining the performance of the inductive type thin film writing magnetic head is a throat height TH. This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible. The reduction of this throat height is also decided by an amount of polishing the air bearing surface.
Therefore, in order to improve the performance of the composite type thin film magnetic head having the writing inductive type thin film magnetic head and reading magnetoresistive type thin film magnetic head stacked one on the other, it is important that the recording inductive type thin film magnetic head and reproducing magnetoresistive type thin film magnetic head are formed with a good balance.
FIGS. 1-9 show successive steps for manufacturing a conventional standard thin film magnetic head, in these drawings A depicts a cross-sectional view of a substantial portion of the head and B represent a cross sectional view of a pole portion. Moreover, FIGS. 10-12 are a cross sectional view of a substantial portion of the completed thin film magnetic head, a cross sectional view of the pole portion, and a plan view of the substantial portion of the thin film magnetic head, respectively. It should be noted that the thin film magnetic head is of a composite type in which the inductive type thin film magnetic head for writing is stacked on the reproducing MR element.
First of all, as shown in FIG. 1, an insulating layer 2 consisting of, for example alumina (Al.sub.2 O.sub.3) is deposited on a substance 1 made of a non-magnetic and electrically insulating material such as AlTiC and having a thickness of about 5-10 .mu.m. Next, as shown in FIG. 2, a first magnetic layer 3 which constitutes one of magnetic shields protecting the MR reproduction element of the reproducing head from the influence of an external magnetic field, is formed with a thickness of 3 .mu.m. Afterwards, as shown in FIG. 3, after depositing an insulating layer 4 of thickness 100-150 nm serving as a shield gap layer by spattering alumina, a magnetoresistive layer 5 made of a material having the magnetoresistive effect and constituting the MR reproduction element is formed on the shield gap layer with a thickness of several tens nano meters and is then shaped into a given pattern by the highly precise mask alignment.
Then, as shown in the FIG. 4, an insulating layer 6 is formed such that the magnetoresistive layer 5 is embedded within the insulating layers 4 and 6.
Next, as shown in the FIG. 5, a second magnetic layer 7 made of a permalloy is formed with a film thickness of 3 .mu.m. This second magnetic layer 7 has not only the function of the upper shield layer which magnetically shields the MR reproduction element together with the above described lower shield layer 3, but also has the function of one of poles of the writing thin film magnetic head.
Then, after forming a write gap layer 7 made of a non-magnetic material such as alumina and having a thickness of about 200 nm on the second magnetic layer 7, a pole chip 9 made of a material having a high saturation magnetic flux density such as permalloy (Ni:50 wt %, Fe:50 wt %) and nitride iron (FeN) is formed with a desired shape by the highly precise mask alignment. A track width is determined by a width W of the pole chip 9. Therefore, in order to realize a high surface recording density, it is necessary to decrease the width W. In this case, a dummy pattern 9' for coupling the bottom pole (first magnetic layer) with the top pole (third magnetic layer) is formed simultaneously. Then, a through-hole can be easily formed by polishing or chemical mechanical polishing (CMP).
In order to prevent an effective width of writing track from being widened, that is, in order to prevent a magnetic flux from being spread at the bottom pole upon the data writing, portions of the gap layer 8 and second magnetic layer 7 constituting the other pole surrounding the pole chip 9 are etched by an ion beam etching such as ion milling. The structure after this process is shown in FIG. 5. This structure is called a trim structure and this portion serves as a pole portion of the first magnetic layer.
Next, as shown in FIG. 6, after forming an insulating layer, for example alumina film 10 with a thickness of about 3 .mu.m, the whole surface is flattened by, for instance CMP. Subsequently, after forming an electrically insulating photoresist layer 11 into a given pattern by the mask alignment of high precision, a first layer thin film coil 12 made of, for instance copper is formed on the photoresist layer 11. Continuously, as shown in FIG. 7, after forming an electrically insulating photoresist layer 13 on the thin film coil 12 by the highly precise mask alignment, the photoresist layer is sintered at a temperature of, for example 250-300.degree. C.
In addition, as shown in FIG. 8, a second layer thin film coil 14 is formed on the flattened surface of the photoresist layer 13. Next, after forming a photoresist layer 15 on the second layer thin film coil 14 with the highly precise mask alignment, the photoresist layer is flattened by performing the sintering process at a temperature of, for example 250.degree. C. As described above, the reason why the photoresist layers 11, 13 and 15 are formed by the highly precise mask alignment process, is that the throat height and MR height are defined on the basis of a position of the edges of the photoresist layers on a side of the pole portion.
Next, as shown in FIG. 9, a third magnetic layer 16 made of, for example a permalloy and having a thickness of 3 .mu.m is selectively formed on the pole chip 9 and photoresist layers 11, 13 and 15 in accordance with a desired pattern.
This third magnetic layer 16 is coupled with the first magnetic layer 7 at a rear position remote from the pole portion through the dummy pattern 9', and the thin film coil 12, 14 passes through a closed magnetic circuit composed of the second magnetic layer, pole chip and third magnetic layer. Furthermore, an overcoat layer 17 made of alumina is deposited on the exposed surface of the third magnetic layer 16.
Finally, a side surface of an assembly at which the magnetoresistive layer 5 and gap layer 8 are formed is polished to form an air bearing surface (ABS) 18 which is to be opposed to the magnetic record medium. During the formation of the air bearing surface 18, the magnetoresistive layer 5 is also ground to obtain a MR reproduction element 19. In this way, the above described throat height TH and the MR height MRH are determined. This condition is shown in FIG. 10. In an actual thin film magnetic head, electric conductors and contact pads for performing the electrical connection to the thin film coils 12, 14 and MR reproduction element 19 are formed, but they are not shown in the drawings.
As shown in FIG. 10, an angle .theta. (apex Angle) between a line S connecting side corners of the photoresist layers 11,13,15 for isolating the thin film coils 12,14 and the upper surface of the third magnetic layers 16 is an important factor for determining the performance of the thin film magnetic head together with the above described throat height TH and MR height.
Moreover, as shown in the plan view of FIG. 12, the width W of the pole chip 9 and a pole portion 20 of the third magnetic layer 16 is small. Since the width of the track recorded on the magnetic record medium is defined by this width W, it is necessary to narrow this width as small as possible in order to achieve a high surface recording density. It should be noted that in this figure, for the sake of convenience, the thin film coils 12, 14 are shown concentrically.
In the method of manufacturing the conventional thin film magnetic head, there is a problem that after forming the thin film coil, the top pole could not be formed precisely on the protruded coil section covered with the insulating photoresist especially along the inclined surface (apex).
That is to say, in the known method, the third magnetic layer is formed by first plating a magnetic material such as permalloy on the mountain shaped coil with a height of about 7-10 .mu.m, by applying the photoresist with a thickness of 3-4 .mu.m, and by shaping the magnetic layer into a given pattern by means of the photolithography technology. Now it is assumed that the photoresist formed on the protruded coil portion into a given pattern should have a thickness of 3 .mu.m or more, a thickness of the photoresist at a bottom or root of the inclined portion would amount to about 8-10 .mu.m. On the one hand, the third magnetic layer formed on the protruded coil portion having a height of about 10 .mu.m as well as on the write gap layer formed on the flat surface should have a narrow portion in the vicinity of the edges of the insulating photoresist layers (for instance layers 11 and 13 in FIG. 7) in order to realize a narrow track width. Therefore, it is necessary to form the pattern having a width of 1 .mu.m by using the photoresist film having a large thickness of 8-10 .mu.m.
However, it is extremely difficult to form the photoresist film having a thickness of 8-10 .mu.m into a pattern having a width of about 1 .mu.m, because upon the light exposure in the photolithography, a pattern deformation might occur due to reflection of light and resolution is reduced due to the thick photoresist layer. In this manner, it is extremely difficult to form a top pole defining precisely a narrow track width by patterning. Then, as is shown in the above explained conventional thin film magnetic head, in order to write data by means of the pole chip capable of forming the narrow track width, after forming the pole chip, the top pole is formed to be connected to the pole chip. In other words, in order to solve the above problem, a divided structure is adopted, that is, the pole chip for determining the track width and the third magnetic layer for introducing the magnetic flux.
However, the known thin film magnetic head, particularly the recording head formed as in the above manner still has the following problems.
(1) Since a positional relation between the pole chip 9 and the third magnetic layer 16 is determined by the alignment of the photoresist layer, a center line of the pole chip viewed from the air bearing surface might deviate largely from a center line of the third magnetic layer, and thus the magnetic flux might leak. Then, the data writing might be carried out by means of the magnetic flux leaked from the third magnetic layer, and the effective track width might be increased and data might be erroneously recorded on an adjacent track. In order to avoid such a problem, it is necessary to increase a distance between successive tracks. Then, the surface recording density could not be improved.
(2) Since the pole chip 9 having a narrow width is brought into contact with the wider third magnetic layer 16 at right angles, the magnetic flux is liable to be saturated at the contact portion, and therefore a satisfactorily high writing characteristic (Flux Rise Time) could not be obtained.
(3) The throat height TH and MR height are determined by taking a position of the edge of the insulating layer isolating the thin film coil on a side of the pole portion as a reference position, but the insulating layer is usually made of an electrically insulating organic photoresist layer and is liable to be deformed by heat. During the formation of the thin film coil, the insulating layer might be deformed by the heating treatment at about 250.degree. C., and a pattern size of the insulating layer changes, and the throat height TH and MR height might be deviated from desired design values.
(4) In the reading thin film magnetic head including the magnetoresistive element, it is advantage to use GMR element having a higher sensitivity, but the reading sensitivity of the GMR element degrades by the heating treatment at about 250.degree. C. for the photoresist layer during the formation of the thin film coil of the inductive type thin film magnetic head.
(5) The high sensitivity GMR element has such a structure that different kinds of very thin layers of thickness 1-5 nm are stacked on each other. Thus, during many steps which are required to complete the composite type thin film magnetic head after the formation of the GMR element, the MR element might be destroyed by electrostatic charge during the handling, and therefore a manufacturing yield might be disadvantageously decreased.
(6) At a nearly finishing stage of the mass production process of the composite type thin film magnetic head, the thick alumina film having a thickness not less than 30-40 .mu.m is formed as the overcoat layer for protecting the head and stabilizing the quality. Due to this thick layer, the substrate is liable to be bent. Furthermore, there might be produced many particles during the spattering process. Consequently characteristics of the magnetic head are degraded and defective magnetic heads might be produced. Moreover the formation of the thick alumina film by spattering requires a long time up to 15 hours or more, and therefore the throughput is extremely decreased. Furthermore, the etching process for exposing the contact pads connected to the magnetoresistive element via the electrode pattern takes a disadvantageously long time.
(7) In the composite type thin film magnetic head, the performance of the thin film magnetic head is mainly determined by the width and MR height of the magnetoresistive element of the magnetoresistive type thin film magnetic head, and by the width of the magnetic pole, throat height and NLTS (Non-Linear Transition Shift) of the inductive type thin film magnetic head. Therefore, demands of users are focused to these parameters. For example, the width of the magnetoresistive element may be designated by users as particular specifications. Since this dimension is determined at an early stage in the manufacturing process of the conventional composite type thin film magnetic head, a time from an order to a supply of products, i.e. the cycle time is prolonged, and sometimes amounts to 30-40 days.